Naitanui hasn't played since suffering an anterior cruciate ligament injury in his left knee against Hawthorn in August last year.

There's always been some hope that the influential ruckman could return late in the 2017 AFL regular season, with a view to a finals impact but Simpson said that's becoming unlikely.

"He's a small chance. It's getting smaller by the week," Simpson told Fox Sports News.

"He's going to travel overseas and do some intensive rehab, and that was always the plan.

"We were hoping to do that earlier in the year but at this stage it's getting pretty difficult.

"Once he gets back from overseas, we'll make a call on it but it's getting towards the end of the year and it's going to be pretty tough for him."

Naitanui will head to the United States to work with sports injury expert Bill Knowles.